According to DOS (German Published Specification) No. 2,726,662, silanes or epoxides are employed as costabilizers in specific polycarbonates stabilized by phosphites.
According to DOS (German Published Specification) No. 2,659,756, siloxanes and, if appropriate, epoxide compounds are employed for stabilizing polycarbonates stabilized by phosphites.
According to DOS (German Published Specification) No. 2,741,064, silanols are employed for stabilizing pigment-containing polycarbonates stabilized by phosphites and/or stabilized by epoxides.
According to DOS (German Published Specification) No. 2,140,207, phosphites containing oxetane groups are employed for stabilizing polycarbonates.
According to DOS (German Published Specification) No. 2,255,639, phosphites containing oxetane groups are likewise added to stabilize polycarbonates, it also being possible for the phosphites to contain tetrahydrofuryl radicals.
According to DOS (German Published Specification) No. 2,510,463, esters of silicic acid together with oxetane compounds and/or specific dioxane compounds and/or specific tetrahydrofurane compounds can be employed for stabilizing polycarbonates stabilized by phosphites (see pages 4, 5 and 6 of that reference).
According to European Patent Application No. 78 101 260 (LeA 18, 380-EP), esters of salicic acid together with oxetane compounds and/or specific dioxane compounds and/or specific tetrahydrofurane compounds can be employed for stabilizing polycarbonates stabilized by boric acid esters (see pages 5, 15 and 18 of that reference).
According to DOS (German Published Specification) No. 2,658,849, oxetane compounds, optionally together with phosphites, are employed for stabilizing polycarbonates.
According to British Patent Specification No. 1,141,869, silanes which are suitable as transesterification catalysts for the preparation of polycarbonates by the melt transesterification process are those which at the same time have a stabilizing effect and thus do not cause discoloration and clouding of the prepared polycarbonate, a side effect caused by some transesterification catalysts. The silanes employed contain at most one alkoxy-silane radical. According to DE-OS (German Published Specification) No. 1,770,329 and U.S. Pat. No. 3,625,920, such silanes can also be employed together with borates, as transesterification catalysts for the same purpose.
However, from these literature references it cannot be deduced that the addition of organic silicon compounds to polycarbonates, in particular to those which are prepared by the solution process, have a brightening, in addition to a stabilizing effect vis degradation upon exposure to heat.
In U.S. Pat. No. 4,138,379, silanes, optionally in combination with phosphites and/or epoxides, are claimed as additives to increase the melt flow and as stabilizers towards oxidative degradation under heat. In all the examples of that reference however, a mixture of 1 part of diphenyl octyl phosphite and 2 parts of 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate is also added, so that it is not shown whether the silicon compounds have a sufficiently stabilizing effect by themselves, i.e. without the phosphites which are of little advantage in promoting the hydrolytic properties of polycarbonate. Moreover, a positive effect is described only after processing and not after heat aging for a long period.